Human cytomegalovirus (HCMV) is a ubiquitous herpesvirus that infects the majority of the world's population. Although HCMV infection is usually sub-clinical in healthy individuals it can be a devastating disease in immunocompromised individuals such as neonates, transplant recipients, and AIDS patients. Our research program is focused on elucidating the molecular mechanisms that regulate HCMV replication and pathogenesis. Specifically, our research program is focused on determining what role tegument proteins play in regulating viral replication. Tegument proteins are packaged within virus particles and delivered to the host cell immediately after infection and can function prior to transcription from the viral genome. Using HCMV deletion mutants we have demonstrated that the UL82 and UL69 tegument proteins play critical roles in HCMV replication. UL82 and UL69 are similar in many respects including their ability to regulate viral gene expression, their ability to modulate the host cell cycle and most importantly they are both required for efficient viral replication. However, the mechanism by which these proteins regulate HCMV replication has not been elucidated. This proposal is designed to test the hypothesis that UL82 and UL69's ability to regulate viral gene expression is required for efficient virus replication. By utilizing UL82 and UL69 recombinant viruses and a number of genetic and biochemical approaches we will identify the critical functions associated with UL82 and UL69 and address the following specific aims: 1) elucidate the mechanism by whichpp71 regulates HCMV immediate early gene expression and HCMV replication; 2) elucidate the mechanism by which ppUL69 regulates HCMV late gene expression and HCMV replication; and 3) identify and characterize cellular and/or viral proteins that interact functionally with pp71 or ppUL69. By understanding the function of these tegument proteins and elucidating the mechanism by which they regulate HCMV replication we may be able to identify novel approaches or therapeutics to help combat HCMV infection.